This invention relates to forming emulsions.
We use the term xe2x80x9cemulsionxe2x80x9d for a system comprising two immiscible liquid phases, with one phase dispersed as small droplets in the other phase. For simplicity we will call the dispersed phase xe2x80x9coilxe2x80x9d and the continuous phase xe2x80x9cwaterxe2x80x9d, although the actual components may vary widely. As additional components, emulsifying agents, known as emulsifiers or surfactants, serve to stabilize emulsions and facilitate their formation, by surrounding the oil phase droplets and separating them from the water phase.
The uses of emulsions have been increasing for many years. Most processed food and beverage products, medicine and personal care products, paints, inks, toners, and photographic media are either emulsions or employ emulsions. In recent years, demand for emulsions with smaller and more uniform droplets has increased. Artificial blood applications, for example, require nearly uniform droplets averaging 0.2 micrometers. Jet-ink printing has similar requirements of size and distribution.
High pressure homogenizers are often used to produce small and uniform droplets or particles, employing a device which is commonly referred to as an homogenizing valve. The valve is kept closed by a plug forced against a seat by means of a spring or hydraulic or pneumatic pressure. The pre-mixed raw emulsion is fed at a high pressure, generally between 1,000 and 15,000 psi, to the center of the valve seat. When the fluid pressure overcomes the force closing the valve, a narrow annular gap (10-200 um) is opened between the valve seat and the valve plug. The raw emulsion flows through, undergoing rapid acceleration as well as sudden drop in pressure which breaks down the oil phase into small droplets. More recently, a new type of high pressure homogenizer was introduced, employing two or more fixed orifices, and capable of reaching 40,000 psi. When forced through these orifices, the pre-mixed raw emulsion forms liquid jets which are caused to impinge at each other. A description is found in U.S. Pat. Nos. 4,533,254 and 4,908,154.
The typical mechanism for emulsification in this type of device is the controlled use of shear, impact, and cavitation forces in a small zone. The relative effects of these forces generally depend on the fluid""s characteristics, but in the vast majority of emulsion preparation schemes, cavitation is the dominant force.
Fluid shear is created by differential velocity within the fluid stream, generated by the sudden fluid acceleration upon entering the orifice or small gap, by the difference between the extremely high velocity at the center of the orifice and zero velocity at the surfaces defining the orifice, and by the intense turbulence which occurs after exiting the orifice.
Cavitation takes place when pressure drops momentarily below the vapor pressure of the water phase. Small vapor bubbles form and then collapse (within 10-3 to 10-9 sec.), generating shock waves which break down surrounding oil droplets. Cavitation occurs in homogenizing valves when the sudden acceleration in the orifice, with a simultaneous pressure drop, causes the local pressure to drop momentarily below the vapor pressure.
More generally, it has become known that cavitation occurs when two surfaces are separated faster than some critical velocity, and that cavitation bubbles affect their surrounding only during the formation of the cavities, and not during the collapse of the cavities, as had been long assumed. Another discovery of interest is that cavitation can occur either totally within the liquid, or at the solid-liquid interfaces, depending on the relative strength of solid-liquid adhesion and the liquidxe2x80x94liquid cohesion.
Typical emulsification schemes have several characteristics worth noting. Cavitation takes place only once, for a very short time (10-3 to 10-9 seconds), and equipment which employs high power density imparts emulsification energy only to a very small portion of the product at any given time. The emulsification process is thus highly sensitive to the uniformity of the feed stock, and several passes through the equipment are usually required before the desired average droplet size and uniformity are achieved. The final droplet size depends on the surfactant""s rate of interaction with the oil phase. Because surfactants cannot generally surround the oil droplets at the same rate they are being formed by the emulsifying process, agglomeration takes place and average droplets size increases. There is a typical sharp increase in product temperature during the process, which limits the choice of emulsion ingredients and processing pressure, as well as accelerating the agglomeration rate of the droplets after the emulsification process. Some processes require very small solid polymer or resin particles; and this is often accomplished by dissolving solid polymers or resins in VOC""s (volatile organic compounds), then employing mixing equipment to reduce the droplets size, and finally removing the VOC.
In general, in one aspect, the invention features a method for use in causing emulsification in a fluid. In the method, a jet of fluid is directed along a first path, and a structure is interposed in the first path to cause the fluid to be redirected in a controlled flow along a new path, the first path and the new path being oriented to cause shear and cavitation in the fluid.
Implementations of the invention may include the following features.
The first path and the new path may be oriented in essentially opposite directions. The coherent flow may be a cylinder surrounding the jet. The interposed structure may have a reflecting surface that is generally semi-spherical, or is generally tapered, and lies at the end of a well. Adjustments may be made to the pressure in the well, in the distance from the opening of the well to the reflecting surface, and in the size of the opening to the well. The controlled flow, as it exits the well, may be directed in an annular sheet away from the opening of the well. An annular flow of a coolant may be directed in a direction opposite to the direction of the annular sheet.
In general, in another aspect, the invention features a method for use in stabilizing a hot emulsion immediately after formation. The emulsion is caused to flow away from the outlet end of an emulsion forming structure, and a cooling fluid is caused to flow in a direction generally opposite to the flow of the emulsion and in close enough proximity to exchange heat with the emulsion flow.
Implementations of the invention may include the following features. The emulsion may be formed as a thin annular sheet as it flows out of the emulsion forming structure. The cooling fluid may be a thin annular sheet as it flows opposite to the emulsion. The cooling fluid may be a liquid or gas compatible with the emulsion. The flows of the emulsion and the cooling fluid may occur in an annular valve opening.
In general, in another aspect, the invention features a method for use in causing emulsification of a first fluid component within a second fluid component. In the method, an essentially stagnant supply of the first fluid component is provided in a cavity. A jet of the second fluid component is directed into the second fluid component. The temperatures and the jet velocities of the fluids are chosen to cause cavitation due to hydraulic separation at the interface between the two fluids.
Implementations of the invention may include the following features. The second fluid component may include a continuous phase of an emulsion or dispersion. The first fluid component may be a discontinuous phase in the emulsion, e.g., a solid discontinuous phase. The second fluid may be provided in an annular chamber, and the jet may be delivered from an outlet of an orifice which opens into the annular chamber. After emulsification by hydraulic separation, the product may be passed through an orifice to cause additional emulsification, or may be delivered to a subsequent processing chamber, where an additional component may be added to the emulsion. A cooling fluid may be applied to the product in the subsequent processing chamber to quickly cool and stabilize the emulsion. The subsequent processing chamber may be an absorption cell into which a jet of the product is directed.
In general, in another aspect, the invention features an apparatus for reducing pressure fluctuations in an emulsifying cell fed from a fluid line by a high pressure pump. A coiled tube in the fluid line between the pump and the emulsifying cell has internal volume, wall thickness, coil diameter and coiling pattern adequate to absorb the pressure fluctuations and capable of withstanding the high pressure generated by the pump. The apparatus may include a shell around the coiled tube with ports for filling the shell with heating or cooling fluid.
In general, in another aspect, the invention features a nozzle for use in an emulsification structure. In the structure, two body pieces having flat surfaces mate to form the nozzle, at least one of the members having a groove to form an orifice in the nozzle. The surfaces are sufficiently flat so that when the two body pieces are pressed together with sufficient force, fluid flow is confined to the orifice. In implementations of the invention, the cavitation inducing surfaces may be defined on the groove; and a wall of the groove may be coated with diamond or non-polar materials or polar materials.
In general, in another aspect, the invention features an absorption cell for use in an emulsification structure. The cell includes an elongated chamber having an open end for receiving a jet of fluid having two immiscible components. A reflective surface is provided at the other end of the chamber for reflecting the jet. And a mechanism is provided for adjusting the distance from the reflective surface to the open end.
Implementations of the invention may include the following features. The reflective surfaces may be interchangeable for different applications. There may be a removable insert for insertion into the chamber at the open end, the insert having an orifice of a smaller dimension than the inner wall of the chamber. There may be several different inserts each suitable for a different application.
In general, in another aspect, the invention features a modular emulsification structure comprising a series of couplings that can be fitted together in a variety of ways. Each of at least one of the couplings includes an annular male sealing surface at one end of the coupling, and an annular female sealing surface at the other end of the coupling. An opening is provided between the male and female sealing surfaces, for communicating fluid from a up-stream coupling to a down-stream coupling. Ports are provided for feeding fluid into or withdrawing fluid from the coupling. At least some of the communicating openings are sufficiently small to form a liquid jet. The sealing surfaces are sufficiently smooth to provide a fluid-tight seal when the couplings are held together by a sufficient compressive force directed along the length of the structure.
Implementations of the invention may include the following features. A processing chamber may be defined between the male sealing surface of one of the up-stream couplings and the female sealing surface of one of the down-stream couplings. In some of the couplings, the orifice may extend from one end of the coupling to the other. An absorption cell coupling may be used at one of the structure. One of the couplings may extend into another coupling to form a small annular opening for generating an annular flow sheet of cooling fluid. Some of the ports in the couplings are used for CIP/SIP cleaning and/or sterilization procedures.
Advantages of the invention include the following.
Very small liquid droplets or solid particles may be processed in the course of emulsifying, mixing, suspending, dispersing, or de-agglomerating solid and/or liquid materials. Nearly uniform sub-micron droplets or particles are produced. The process is uniform over time because pressure spikes that are normally generated by the high pressure pump are eliminated. A broader range of types of emulsion ingredients may be used while maximizing their effectiveness by introducing them separately into the high velocity fluid jet. Fine emulsions may be produced using fast reacting ingredients, by adding each ingredient separately and by controlling the locations of their interaction. Control of temperature before and during emulsification allows multiple cavitation stages without damaging heat sensitive ingredients, by enabling injection of ingredients at different temperatures and by injecting compressed air or liquid nitrogen prior to the final emulsification step. The effects of cavitation on the liquid stream are maximized while minimizing the wear effects on the surrounding solid surfaces, by controlling orifice geometry, materials selection, surface characteristics, pressure and temperature. Absorption of the jet""s kinetic energy into the fluid stream is maximized, while minimizing its wear effect on surrounding solid surfaces. A sufficient turbulence is achieved to prevent agglomeration before the surfactants can fully react with the newly formed droplets. Agglomeration after treatment is minimized by rapid cooling, by injecting compressed air or nitrogen and/or by rapid heat exchange, while the emulsion is subjected to sufficient turbulence to overcome the oil droplets"" attractive forces and maintaining sufficient pressure to prevent the water from vaporizing.
Scale-up procedures from small laboratory scale devices to large production scale systems is made simpler because every process parameter can be carefully controlled. The invention is applicable to emulsions, microemulsions, dispersions, liposomes, and cell rupture. A wide variety of immiscible liquids may be used, in a wider range of ratios. Smaller amounts of (in some cases no) emulsifiers are required. Emulsions can be produced in one pass through the process. The reproducibility of the process is improved. A wide variety of emulsions may be produced for diverse uses such as food, beverages, pharmaceuticals, paints, inks, toners, fuels, magnetic media, and cosmetics. The apparatus is easy to assemble, disassemble, clean, and maintain. The process may be used with fluids of high viscosity, high solid content, and fluids which are abrasive and corrosive.
The emulsification effect continues long enough for surfactants to react with newly formed oil droplets. Multiple stages of cavitation assure complete use of the surfactant with virtually no waist in the form of micelles. Multiple ports along the process stream may be used for cooling by injecting ingredient at lower temperature. VOC""s may be replaced with hot water to produce the same end products. The water will be heated under high pressure to well above the melting point of the polymer or resin. The solid polymer or resins will be injected in its solid state, to be melted and pulverized by the hot water jet. The provision of multiple ports eliminates the problematic introduction of large solid particles into the high pressure pumps, and requires only standard industrial pumps.
Other advantages and features will become apparent from the following description and from the claims.